Characterization of Herbicide- Resistant Biotypes of Barnyardgrass

Barnyardgrass (Echinochloa crus-galli) biotypes, resistant to different herbicides, have been reported. An experiment was conducted to compare the growth characteristics of various barnyardgrass biotypes, (i.e., propanil-resistant from Poinsett County, Ark., quinclorac-resistant from Louisiana., quinclorac/propanil-resistant barnyardgrass from Craighead County, Ark., and susceptible barnyardgrass from Arkansas County) with the rice cultivar ‘Wells’ in a non-competitive environment at Stuttgart, Ark., in 2002 and 2003. Seeds were planted in the greenhouse and 28 seedlings of each barnyardgrass biotype and rice were transplanted into separate plots at 3 ft spacing. The top growth of four plants was harvested weekly and growth characteristics including height, number of tillers, leaf area, and dry weights were recorded at 4 to 10 weeks after emergence. The quinclorac-resistant barnyardgrass from Louisiana had a prostrate growth habit as compared to other barnyardgrass biotypes. There was no significant difference among the growth of barnyardgrass biotypes, but the growth of barnyardgrass was significantly different from rice. The quinclorac-resistant biotype was also taller than the others with an average height of 47 in., while rice was 28 in. tall. The quinclorac/propanil-resistant barnyardgrass produced 6 times more tillers (210) than rice (30) and the leaf area and biomass of barnyardgrass biotypes was about 9 times higher than rice. In addition, the quinclorac/propanil-resistant biotype had a leaf area of 852.5 in.2/plant and a biomass of 1.54 lb/plant as compared to 99 in.2/plant and 0.18 lb/plant in rice, 11 weeks after emergence.